Concentration process



June 10, 1969 R.G.REIIMUS ET L CONCENTRATION PROCESS Original Fild Dec.2, 1965 2 2 2 (/7711 [/475 rPKrMzz/zz/ 5P4J70P United States Patent US.Cl. 99-71 6 Claims ABSTRACT OF THE DISCLOSURE A process is described forthe concentration of coffee liquid by partially freezing ice therein andseparating the ice from the concentrated liquid. Prior to freezing theice, the liquid is chilled to a temperature range from about 45 to 80 F.to form a mixture of Waxes and similar material and liquid coffeeextract and the mixture is treated so that waxes and similar materialare removed from the liquid before the ice is formed.

This application is a division of our copending application Ser. No.718,510 filed Apr. 3, 1968, which is a division of Ser. No. 511,173, nowPatent No. 3,381,302.

This invention relates to an improvement in a process for thepreparation of concentrated comestible liquids and liquid extracts andis particularly applicable to the preparation of soluble coffee solidsor powdered coffee. More particularly, this invention relates to thepre-treatment of liquids and liquid extracts as a step preliminary toremoval of water from the extract by a freezing process.

Soluble, or powdered, coffee has been prepared by first extractingcoffee beans with hot Water and subsequently dehydrating the extract byspray drying under vacuum conditions. This process has met with vastcommercial success, but the flavor of the soluble coffee leaves much tobe desired. The vacuum conditions employed not only remove water fromthe extract, but also cause volatile taste and flavor elements of thecoffee to evaporate. The resulting soluble product is, therefore, neveras good as the extract from which it is prepared.

To improve the flavor of the soluble cofiee, it has been often proposedto remove substantial amounts of water in the extract by partiallyfreezing the extract and separating the resulting pure ice crystals fromthe concentrated extract. This process of partial freezing is thenfollowed by a complete dehydration by evaporation of water which may beconducted under vacuum conditions. In this way, the coffee loses less ofthe volatile components by virtue of the fact that the extract issubject to evaporation conditions for shorter periods of time.

In a preferred embodiment of the freezing process, the coffee extract ispartially frozen by indirect refrigeration in a suitable crystallizerand the resulting slurry of ice and concentrate is subjected tocentrifugation to separate the ice from the concentrate. In order forthe process to be economical, this separation and the subsequent waterwash of the crystals on the centrifuge basket must effect a relativelycomplete removal of mother liquor from the ice crystals.

However, when coffee extract is cooled to near its initial freezingpoint, a gummy or waxy solid material often precipitates from solutionprior to ice formation. This wax or tar is carried along with the icecrystals and coffee extract into the centrifuge and collects on thecentrifuge basket, eventually plugging the basket and preventing thecomplete separation of ice from concentrated extract.

This problem of the precipitation of insoluble materials in the coffeeextract is not a problem exclusive to coffee extracts alone, but is alsoencountered in the preparation of other concentrated extracts ofcomestible materials. Thus, the process of this invention is alsoapplicable to the preparation of concentrated extracts of suchcomestible materials as the tea, grape juice, apple juice, beer andorange juice.

It is therefore an object of this invention to provide an improvedprocess for the concentration of comestible liquids and liquid extractsby partial freezing of the liquid or liquid extracts.

Another object of this invention is to provide a process in which acomestible liquid or liquid extract, free of insoluble elements at thefreezing temperature of ice, is subjected to freeze concentration.

Yet another object of this invention is to provide an improved processfor the concentration of coffee extract by partial freezing of theextract.

Still another object of this invention is to provide a process in whichcoffee extract, free of insoluble elements at the freezing temperatureof ice, is subjected to freeze concentration.

The objects of this invention are accomplished by a process whichcomprises preparing a comestible liquid or liquid extract, cooling theliquid to precipitate material insoluble at the temperature at which iceforms therein, removing insolubles from the resulting mixture and thensubjecting the insoluble-free mixture to concentration by partialfreezing of water therefrom.

A preferred embodiment of this invention is a process which comprisesextracting coffee beans at elevated temperatures with Water to produce acoffee extract, cooling the extract to precipitate materials insolubleat the temperature at which ice forms in the brew, removing insolublesfrom the resulting mixture and then subjecting the insoluble freemixture to concentration by partial freezing of water therefrom.

The initial steps in the process of preparing instant coffee are thesame as preparing regular coffee. Following roasting, the coffee isground, but the granulation may be extremely coarse and, in some cases,fine particles that may result from grinding are sieved out and usedelsewhere.

The grounds are placed in closed containers 'known as extractors. Theseextractors are set up in batteries with several extractors to a battery.

Ground coffee and hot water are charged into the first extractor. Thecoffee is then extracted until the necessary materials have been removedfrom the grounds. The resulting extract is then charged into the secondextractor containing fresh coffee. The second extractor is run untilextraction is completed. The resulting coffee extract (which is nowstronger than ordinary coffee beverage) is placed in the third extractorcontaining fresh grounds and the brewing process is again repeated.

In commercial plant operation, the process is conducted in asemi-continuous manner, the fresh water coming into an extractionbattery first reaches the extractor having the most spent, exhaustedgrounds and proceeds from there to the next most spent grounds and so onuntil, finally, in the last extractor it reaches the fresh, mostrecently added grounds. This is known as a coutnercurrent extractionsystem.

Temperature and pressure in the extractor system will vary greatly.Coffee being produced from fresh grounds is usually processed at lowtemperature with low pressure. Coffee being produced from spent,exhausted grounds is extracted at high temperature and under highpressure.

The coffee extract to be concentrated by freeze concentration can haveany coffee solids content from a few percent to as high as 40 to 50percent. That is, there may be as much as 40 to 50 lbs. of coffee solidsin the extract for each 100 lbs. of extract. However, the lower thesolids content of extract, the more the water which must be removedduring the freeze concentration and drying steps. On the other hand, ithas been found that carrying the extraction process to the point wherehigh coffee solids content can be achieved often lowers the fiavorquality of the extract. Thus, a preferred range of coffee solids contentof the extract for the practice of this invention is from about to 30percent coffee solids.

In prior art processes, after leaving the extractor system, the coffeeextract is clarified of sediment while still at an elevated temperature.One of the most common methods of clarification is by means of acentrifuge in which the coffee liquid is passed through a rapidlyrotating cylinder and discharges the clear liquid. Another method is bymeans of a pressure pump forcing the concentrate through porous paper orcloth.

However, according to one embodiment of the process of this invention,the hot coffee extract is first chilled to near the freezing point sothat waxes, tars and gums which are soluble in the hot extract areprecipitated therefrom. The cold extract is then subjected to filtrationor centrifugation to free it, not only of the precipitated gums, tarsand waxes, but also from any sediment resulting from the extractionprocess.

Because the initial freezing point of the coffee extract is dependent onthe total coffee solids content of the ex tract, the temperature towhich the extract should be chilled to precipitate the gums, tars andwaxes varies with the exact nature of the extract. Ordinarily, howevermini mum temperatures of 40 F. and below may be employed in the processof this invention. If it is not desired to form ice in the extractduring the precipitation process, the tem' perature to which the extractis chilled should not be below the initial freezing point. For a coffeeextract hav ing 30 wt. percent coffee solids, the temperature is about27 F.

In practice, it has been found that the tars, waxes and gums will beginto precipitate from coffee at temperatures as high as about 80 F. andthat the major portion of insolubles will precipitate at temperaturesabove 32 F. Thus, an embodiment of this invention comprises chilling theextract to between 80 and 32 F. prior to filtration and freezeconcentration. Preferred temperatures for the chilling operation arebetween about 45 and 32 F. because this temperature range insuresvirtually complete removal of insolubles.

The coffee extract may be chilled by any convenient means. However, itis preferred to keep the extract under agitation so that the wax andgums formed during the precipitation step do not adhere to the heattransfer surface of the refrigeration means used to precipitate. Ifdesired, the chilled extract may be held at the low temperature for froma few seconds to several or many hours before the waxes, tars and gumsare removed, either by centrifugation or filtration. The formation andprecipitati n f t s. g ms a d waxes is o te time-d p de t a d completeprecipitation may require holding the material at the low temperatureemployed until the process is complete. Thus, when conducting theprocess of this invention in a continuous fashion, the time elapsedbetween the chilling to precipitate waxes and actual separation of thewaxes, tars and gums from the chilled coffee extract will depend on theexact nature of the extract.

In some coffee extracts, continued exposure to low temperature will alsocause the formation of a non-waxey particulate precipitate. Thisparticulate precipitate forms after the formation of insoluble tars,waxes and gums and does not interfere with the centrifugal separation ofice from concentrated coffee extract after the freeze concentrationprocess. However, such exposure to low temperatures sufficient to causethis particulate precipitate should be avoided because it is tantamountto degradation of the coffee extract. The resulting concentratedproduct, after this degradation, is not as satisfactory to the consumeras coffee produced from extract which has been chilled only sufficientlyto cause the precipitation of tars, gums and waxes.

Depending upon the exact nature of the coffee blend employed inpreparing the extract and the extract itself, from less than 0.5 toabout 5 percent by weight of tars, gums and waxes will form during theprecipitation step. Although most of the gums, waxes and tars which willform from the coffee extract form at near the initial freezing point ofthe extract, more may form after the extract is subjected to freezeconcentration. Thus, another embodiment of this invention comprisescooling the coffee extract to below the initial freezing temperature toprecipitate the insoluble wax, tar or gum and forming a minor amount ofice in the extract. The extract can then be freed of the waxes and tarsby filtration, decantation or centrifugation. In this embodiment of theinvention, the minor portion of ice formed can be removed along with thewaxes and tars, or the extract can be slightly warmed to allow the iceto melt prior to removal of the waxes and tars by filtration,decantation or centrifugation.

The tars, waxes or gums produced by the chilling of the coffee extractcan be removed in any convenient fashion as pointed out above. Thechilled extract may be held at the chilled temperature until such timeas the precipitate settles to the bottom of the container and theprecipitatefree portion of the solution can be decanted and thensubjected to further processing. Alternatively, the chilled extract maybe processed in the same manner as hot coffee extract which is to befreed from sediment. Thus, centrifugation, batch or continuous, orpressure filtration techniques; all well known to the art, may beemployed to sep arate the extract from the precipitate.

After being freed from the precipitate, the resulting precipitate-freecoffee extract is then subjected to concentration by partial freezing ofthe water therefrom. This freeze concentration process can be conductedin batch, semicontinuous or continuous apparatus according to methodsknown to the art and improvements of the methods. However, any method ofremoving the water from the coffee extract by crystallization as ice isapplicable to the process of this invention. The resulting slurry of iceand concentrated coffee extract is then subjected to centrifugation tofree the concentrated solution of the ice crystals. The resuling icecrystals are ordinarily washed with water or dilute coffe extract tofree the ice crystals completely of residual mother liquor and thewashings may be returned to the freeze concentration process. Thepractice of this invention has the advantage that the centrifuge basketdoes not become plugged with precipitated tars and waxes and theseparation and washing processes are facilitated in their efficiency.

The freeze concentration of the wax, tar and gum free comestible liquidor extract can be accomplished in either a single stage or in aplurality of stages, each of which comprises a crystallizer in whichheat is removed from he offee ex ract to form a slurry of ice Crystalsand concentrated mother liquor. After each crystallization stage, ice isremoved from the slurry and the concentrated extract either goes tofurther processing in the preparation of soluble or powdered coffee oris further concentrated in a subsequent stage of the freezeconcentration process. The crystallization of ice from the extract ispreferably carried out in a tubular heat exchanger, the outside surfacesof which are cooled by a circulating refrigerant. The internal sectionof the tube is ordinarily fitted with a shaft on which is locatedagitator paddles. Alternatively, a conventional scraped surface tubularheat exchanger may be employed. Any acceptable separating device orcentrifuge may be employed for separating the concentrated coffeeextract from the resulting ice crystals. This centrifuge is thepreferred method for separating ice from the mother liquor andordinarily consists of a rotating basket which contains perforations forallowing passage of the mother liquor. The centrifuge may also beequipped with some means for washing residual mother liquor from the icecrystals.

Referring now to the drawing accompanying this application, an aqueouscomestible extract enters a chilling or cooling apparatus through feedline 11. The chiller may be a conventional refrigeration unit, acontinuous tubular heat exchanger or the chilling operation may beconducted in a batch manner by placing containers of extract in arefrigerated room. The chilled extract is then fed to the filter 12through line 13. The filter apparatus may be a conventional batchfiltration unit or, where the precipitated wax or tar can be handled ona centrifuge basket, may comprise a rotating basket centrifuge orordinary laboratory or batchtype centrifuge. The filtered extract; nowfree of tars, gums and waxes; is conveyed through line 14 to the tubularcrystallizer 15 where the temperature is lowered sufficiently to causeice to form in the extract. The exact degree of concentration dependsupon the cooling medium and temperature on the outside of thecrystallizer 12 and the residence time in the crystallizer. Concentratedslurry of ice and mother liquor is then conducted to a separatingapparatus 16 through the line 17. The separating apparatus 16 ispreferably a rotating basket centrifuge in which the basket is an openscreen material which allows concentrated mother liquor to be removedfrom the outside periphery of the centrifuge through the line 18 Whileice, preferably reslurried in either water or feed extract, is removedvia line 19.

As pointed out above, the crystallizing concentration operation may beconducted in a plurality of stages.

The following examples are illustrative of the process of thisinvention.

EXAMPLE 1 A batch of coffee extract containing 24 percent coffee solidswas pre-cooled to below 40 F. and admitted to a tubular heat exchangerhaving an internal agitator. The coffee extract was fed to the heatexchanger at the rate of 3 gallons per minute and coffee extract wasrecirculated around the heat exchanger until ice crystals had formed dueto the cooling internally. Recirculation of slurry and mother liquor wascontinued as coffee extract was fed to the crystallizer, the internalsof which were maintained at a temperature of 27 F. A slurry of ice andcoffee liquor containing about 30 percent coffee solids was thencontinuously removed from the crystallizer and fed to a continuous typerotating basket centrifuge. The centrifuge basket was in the form of aperforated screen which allowed coffee liquor to pass through the icecake, thus separating the ice from the coffee liquor. After 10 minutesof operation, the centrifuge screen plugged with tars and waxes whichwere precipitated from the coffee extract during the cooling andcrystallization process. This caused the operation to stop, due toimproper separation of ice and mother liquor.

This procedure is repeated except that the extract is fed to thecrystallizer without first pre-chilling. Tars and gums form along withthe ice and the centrifuge plugs in the same manner as if the extracthad been pre-chilled.

EXAMPLE 2 The general procedure of Example 1 was repeated except thatthe chilled coffee extract was filtered through fine cheesecloth priorto introduction into the crystallizer. In this filtration process,approximately 1.9 percent of the orignal extract was removed as tars,gums or waxes. The resulting precipitate-free coffee liquor was thenadmitted to the crystallizer vessel and the slurry produced in thecrystallizer was centrifuged continuously. The icemother liquorseparation was not impeded by plugging of the centrifuge screen withprecipitate.

Excellent results are also obtained when coffee liquor to beconcentrated is pre-cooled from to 36 F., and when the extract has from12 to 32 percent coffee solids.

EXAMPLE 3 A tea extract containing 6.8 percent tea solids, at above 80F. after extraction, is cooled in a heat exchanger to 36 F. The cooledmaterial is then filtered through a tfilter press and the resultingtar-free extract is freeze concentrated in a tubular crystallizer. Theresulting iceconcentrated tea slurry is easily separated on a rotatingbasket screen-type centrifuge as described above.

The process of this invention is applicable to an aqueous comestibleliquid material or liquid extract which is to be concentrated byformation of ice and subsequent removal of ice. Thus, the process ofthis invention may be used in connection with the freeze concentrationof coffee, tea, grape juice, orange juice, beer, vinegar and the like.

Although the invention has been described with reference to particularembodiment thereof, it is to be understood that various changes may bemade without departing from the spirit of the invention as defined bythe scope of the appended claims.

What is claimed is:

1. In a process for the concentration of liquid coffee extract, whichforms insoluble precipitate material at above the temperature at whichice forms therein and which contains therein about 10 to 50% dissolvedsolids, comprising partial freezing of said liquid extract to form iceand concentrated liquid extract, the improvement which comprises:chilling said liquid extract to a temperature between about 45 and 80 F.to induce formation of insoluble precipitate material therein; holdingsaid liquid extract in said temperature range until after insolubleprecipitate material forms; removing said insoluble precipitate materialfrom said liquid extract; subsequently subjecting said liquid extract toreduced temperature to form a mixture of ice and concentrated extract;and separating ice from said concentrated extract.

2. The process according to claim 1 in which the liquid extract is keptunder agitation during holding and formation of precipitate.

3. The process according to claim 1 in which the coffee extract to betreated contains about 15% to 30% dissolved solids.

4. A process according to claim 1 in which ice is separated from coffeeextract by centrifugation.

5. A process according to claim 1 in which insoluble precipitate isseparated from coffee extract by centrifugation.

6. A process for preparing a dehydrated coffee beverage product solublein water from a liquid coffee extract containing from about 10% to about50% by weight dissolved solids, some of which form insoluble matter at atemperature above the temperature at which ice forms in the extract,including the steps of:

(a) chilling the extract to a temperature range of from about 80 F. toabout 45 F. and maintaining the extract in the temperature range for aperiod of time suflicient to precipitate at least a portion of theinsoluble matter; (b) removing the precipitated insoluble matter formedwithin the range of about 80 F. to about 45 F. from the extract; and c)then subjecting the extract to dehydration.

References Cited UNITED 8 3,102,036 8/1963 Smith 99- 205 3,362,1981/1968 Cottle et a1 99-199 X OTHER REFERENCES Sivetz et 211.: CoffeeProcessing Technology, Avi Publ.

5 Co., Westport, Conn, vol. 1, 1963, p. 481, copy in Art Unit 172.

Sivetz: Coffee Processing Technology, vol. 2, Avi Publ.

Co., Westport, Conn., 1963, pp. 16 and 148, copy in Art 10 Unit 172.

MAURICE W. GREENSTEIN, Primary Examiner.

US. Cl. X.R.

